Taiwan Patent No. 414930 taught that a MOS tunneling diode has been used in the photo-detector, but the detectable wavelength is restrained to the energy gap of the semiconductor material since the additional pairs of electrons and electrical holes are only produced when the energy of photons is higher than the energy gap of material. If a Si substrate is used, the cutoff wavelength thereof is 1.1 μm; and if a Ge substrate is used, the cutoff wavelength thereof is 1.85 μm. Therefore, the Ge material is preferable if 1.3˜1.55 μm of the photo-detection is desired. However, the application of a whole piece of Ge as substrates is highly expensive.
In addition, U.S. Pat. No. 5,374,564 disclosed a smart-cut process, which utilizes a hydrogen implanting technique to implant the hydrogen ions into the inner layers of the wafer, wherein the implanted depth is controlled by the implanting energy. Then, cut the wafer by means of the cleft characteristic of the implanted hydrogen ions being processed during high temperature. This kind of technique can cut the expensive and whole piece of Ge substrate into a plurality of thin Ge wafers.
Furthermore, in U.S. Pat. No. 6,833,195B1, Intel Corp. first implanted ions into the Ge substrates and activates the surfaces of the Ge and Si substrates, followed by bonding the Ge substrate and the Si substrate. As disclosed in the previous smart-cut process, a Si substrate including a thin Ge layer thereon is obtained.
In Applied Physics Letters 89, 101913 (2006), entitled “Low-temperature fabrication and characterization of Ge-on-insulator structures”, a kind of photo-detector is disclosed. The aim of the invention is to provide a photo-detector structure with a metal-insulator-semiconductor formed on a carrier substrate having a Ge layer and a manufacturing process thereof to lower down the expensive cost of using the Ge material. The above invention provides a photo-detector comprising a carrier substrate, a Ge layer, a first metal electrode, an insulating layer and a second metal electrode. The Ge layer is formed on the carrier substrate and includes a first area and a second area. The first metal electrode is formed on the first area, the insulating layer is formed on the second area, and the second metal electrode is formed on the insulating layer which is formed by means of a low temperature liquid phase deposit technique. Despite the invention utilizes the cheaper SiO2—Si substrate rather than the rare and expensive Ge material, there still exists a problem with a higher amount of dark current. In addition, further cheaper substrates, like glass are more desirable.
Moreover, ISDRS (International Semiconductor Device Research Symposium, 2003) published a paper entitled “MOS Ge/Si Quantum Dot Infrared Photodetectors with Quantum Dot and wetting Layer Responses” where the light currents are also reduced while the problem of the dark currents is improved by of the disclosed methods.
From the above description, it is known that how to provide a photo-detector capable of simultaneously enhancing the light current and reducing the dark current has become a major problem waited to be solved. In order to overcome the drawbacks in the prior art, a manufacturing process for a photo-detector is provided. The particular design in the present invention not only solves the problems described above, but also is easy to be implemented. Thus, the invention has the utility for the industry.